I. Field
The present invention relates generally to data communication, and more specifically to Radio Link Protocols (RLPs) for a wireless communication system.
II. Background
Wireless communication systems are widely deployed to provide various communication services such as voice, packet data, and so on. These systems may be multiple-access systems capable of supporting communication with multiple users by sharing the available system resources. Examples of such multiple-access systems include Code Division Multiple Access (CDMA) systems, Time Division Multiple Access (TDMA) systems, Frequency Division Multiple Access (FDMA) systems, Orthogonal Frequency Division Multiple Access (OFDMA) systems, and so on.
A wireless communication system utilizes a physical layer that transmits data using a coding and modulation scheme selected to achieve a target packet error rate (PER) and latency. The PER may be limited by the coding and modulation scheme selected. Additionally, the PER may be limited by the performance of the feedback at the physical layer. For example, a physical layer negative acknowledgement (NAK) for a packet may be incorrectly decoded as a positive acknowledgement (ACK) 2% of the time, resulting in 2% of the packets being incorrectly acknowledged. The target PER may not be sufficiently low for some applications. For example, a physical layer designed to support voice packets at a PER of 1% and a latency of 40 millisecond (ms) may not efficiently support an HTTP browsing application or an FTP download, either of which may achieve higher throughput and shorter download times with a higher latency and a lower PER physical layer.
Many wireless communication systems employ a Radio Link Protocol (RLP) above the physical layer to provide greater reliability for data transmission. The main purposes of the RLP are (1) to provide retransmission, to improve link reliability and performance, and (2) to provide rate adaptation for packet fragments, in the event of changing channel conditions. The RLP supports retransmission of data in order to achieve a lower PER at the expense of higher latency and jitter than what the physical layer can achieve alone. The RLP typically resides at an interior network entity that is remote from an edge network entity providing over-the-air communication. Consequently, feedback from a receiver to a transmitter for RLP is not efficient and incurs prolonged processing and transmission delays. Furthermore, the signaling for the feedback may not be reliable. These two factors complicate the retransmission of data by the RLP.
There is therefore a need in the art for an efficient RLP to improve data transmission performance.